Traditionally, air filters for heating and cooling systems have been provided in a frame having fixed dimensions. While these pre-sized filters and frames generally correspond to particular heating and cooling system size requirements, they offer no sizing flexibility. Because frame and filter sizes are fixed, vendors must stock a wide variety of sizes to accommodate different requirements. Furthermore, users are unable to make small adjustments in filter and frame size to accommodate particular applications. Therefore, it has been desirable to have adjustable filters and frames.
One solution for the need to provide adjustable filters and frames is provided in U.S. Pat. No. 5,087,276. That patent discloses an adjustable frame composed of four right angle members with each right angle member having two legs. Two of the right angle members are slightly reduced in size to be slidably received within the channels of the larger right angle members in a telescoping fashion. The filter is a multiple layer filter medium having a thin mesh support grid on one face. In order to keep the frame at the desired size, the user must insert keeper pins into holes that are variably spaced across the length and width of the frame. The keeper pins also are pushed through a perimeter portion of the thin mesh support grid to hold the filter in place.
The user-sizable furnace filter and frame assembly disclosed in the '276 patent has some limitations. For example, when the user initially sets or subsequently adjusts the frame, the pins may become separated from the rest of the assembly and lost. Also, the user must be very exacting in trimming the filter and thin mesh support grid. Therefore, it is desirable to have a user adjustable filter frame and grid system that is easy to adjust, and in which the size of the adjustable frame may be set and the filter secured in place without the use of small parts that may become separated from the system and lost.